Release DataConnection when a rety is interupted

We had code that simply set the ApnContexts state to IDLE, but
there was still a connection between ApnContext and DataConnection,
so when looking for a DC, we'd skip this one (it's busy) and when
the rety alarm fires we end up with a second DC attempting to connect
to the same APN.

bug:22410092
Change-Id: Id4ab6a4f1f08588e552e846a1986f93192a72568